Computing systems have been introduced for use in financial industries, nuclear power plants and so on to perform mission-critical tasks. Such computing systems are required to ensure high reliability.
As a method of configuring a highly reliable computing system, a redundant computing system has been proposed in which a system having a certain arithmetic processing function and another system having the same function are prepared and these two systems are operated in synchronization.
This redundant computing system, as shown in FIG. 1 for example, is composed of two systems, namely an arithmetic processing unit (A-system) 80A and an arithmetic processing unit (B-system) 80B, and their outputs are input to an comparator 50 and an output control unit 40. The comparator 50 compares the output values from these two systems. If the values do not match, the comparator 50 determines that there is a failure in either the arithmetic processing unit (A-system) 80A or the arithmetic processing unit (B-system) 80B, and informs the output control unit 40 of the comparison result. In this case, the output control unit 40 stops the output. This enables the redundant computing system to avoid outputting an error outside of the system and to improve its reliability.
Further, a redundant computing system as shown in FIGS. 2 and 3 has been proposed, which has a diagnosis unit (A-system) 31A for diagnosing an arithmetic processing unit (A-system) 80A and a diagnosis unit (B-system) 31B for diagnosing an arithmetic processing unit (B-system) 80B (see Patent Document 1, Japanese Patent No. 3210527). This redundant computing system is configured such that when an error is detected, the diagnosis unit (A-system) 31A and the diagnosis unit (B-system) 31 respectively diagnose the arithmetic processing unit (A-system) 80A and the arithmetic processing unit (B-system) 80B to determine which system is in failure causing the error, and the redundant computing system operates in a degenerate mode with only the system not in failure.